Tube bending has applications in various industries, for example, the automobile and aerospace industries. Existing aircraft require high strength-to-weight ratio of components to satisfy the aircraft's flight performance requirements. Modern aircraft have multiple tubing systems, for example, air-preparing system (APS), anti-icing system (AIS), air conditioning system (ACS), fuel system and separate elements, etc., made of especially thin-walled tubes of aluminum alloys, titanium alloys, and anti-corrosion steels. Therefore, thin-wall tube bending processes play an important role in the aircraft manufacturing process.
For thin-walled structures, especially the ultra-thin-wall tube produces buckling and fracture easily during bending processes. A tube bending method, which bends thin-wall tubes with small bend radii without causing buckling or fracture, is required. Traditionally, tube-bending processes, for example, rotary draw bending, roll bending, compressing bending, tube hydroforming, etc., are commonly used. Conventionally, bending thin-walled tubes with critical bend radius is done using sand. With this approach, numerous wrinkles are formed on the inner surface of the tube. Furthermore, the bending tubes and the pipe bending equipment are filled with sand. A tube bending method, which prevents the formation of wrinkles on the inner surface of the tube, is required.
Alternatively, the tubes are filled with molten bismuth. This method produces better quality tubes but causes many environmental problems. Due to weight restrictions and space limitations of an aircraft, use of thin-walled tubes of aluminum alloys, stainless steel, etc., is preferred in air conditioning systems of the aircraft.
Push bending method is an effective method with low production costs for bending thin-wall tubes with critical bend radius. Rotary-draw bending method is commonly used in the automotive industry. Rotary draw bending is a bending operation where the tube is wrapped around a radius block to form the required bend with or without a mandrel depending on cross section requirements. The main problems faced during the rotary-draw tube bending method, for example, are wrinkling, cross sectional distortion, and tube breakage.
The correct use of the process parameters would help to avoid or minimize these defects. The production of thin-wall tubes with a critical bend radius using this method requires computer numerical control (CNC) machines. This requirement further increases the cost of production. Similarly, hydroforming processes are also capable of producing small radii bends. However, hydroforming requires specialized equipment and hydraulic systems, which again reduces production efficiency. A tube bending method, which produces small radii bends economically and efficiently, is required. Moreover, a tube bending method, which applies a suitable frictional force on the tube to produce a well-formed tube, is required.
Hence, there is a long felt but unresolved need for a tube bending method, which bends thin-wall tubes with small bend radii without causing buckling or fracture. Moreover, there is a need for a tube bending method, which prevents the formation of wrinkles on the inner surface of the tube. Furthermore, there is a need for a tube bending method, which creates minimal spring back in tubes.